PHP has three types of comment syntax: /./ marks block and inline comments; // or # are used for one-line comments. The echo statement is one of several facilities PHP provides to output text. In terms of keywords and language syntax, PHP is similar to the C style syntax. An advanced, custom PHP code checker that searches your code for common, hard to find typos and mistakes; includes a syntax check. PHP and MySQL Tutorials. Follow along with these examples before building your own applications with PHP and MySQL. Find tutorials for beginners and professionals that take you step-by-step through a variety of projects and provide sample code.
Syntax
Constants can be defined using the
const
keyword, or by using the define()-function. While define() allows a constant to be defined to an arbitrary expression, the const
keyword has restrictions as outlined in the next paragraph. Once a constant is defined, it can never be changed or undefined. When using the
const
keyword, only scalar (bool, int, float and string) expressions and constant arrays containing only scalar expressions are accepted. It is possible to define constants as a resource, but it should be avoided, as it can cause unexpected results. The value of a constant is accessed simply by specifying its name. Unlike variables, a constant is not prepended with a
$
. It is also possible to use the constant() function to read a constant's value if the constant's name is obtained dynamically. Use get_defined_constants() to get a list of all defined constants. Note: Constants and (global) variables are in a different namespace. This implies that for example
true
and $TRUE are generally different. If an undefined constant is used an Error is thrown. Prior to PHP 8.0.0, undefined constants would be interpreted as a bare word string, i.e. (CONSTANT vs 'CONSTANT'). This fallback is deprecated as of PHP 7.2.0, and an error of level
E_WARNING
is issued when it happens. Prior to PHP 7.2.0, an error of level E_NOTICE has been issued instead. See also the manual entry on why $foo[bar] is wrong (unless bar
is a constant). This does not apply to (fully) qualified constants, which will always raise a Error if undefined. Note: To check if a constant is set, use the defined() function.
These are the differences between constants and variables:
- Constants do not have a dollar sign (
$
) before them; - Constants may be defined and accessed anywhere without regard to variable scoping rules;
- Constants may not be redefined or undefined once they have been set; and
- Constants may only evaluate to scalar values or arrays.
Example #1 Defining Constants
<?php
define('CONSTANT', 'Hello world.');
echo CONSTANT; // outputs 'Hello world.'
echo Constant; // Emits an Error: Undefined constant 'Constant'
// Prior to PHP 8.0.0, outputs 'Constant' and issues a warning.
?>
Example #2 Defining Constants using the
const
keyword<?php
// Simple scalar value
const CONSTANT = 'Hello World';
echo CONSTANT;
// Scalar expression
const ANOTHER_CONST = CONSTANT.'; Goodbye World';
echo ANOTHER_CONST;
const ANIMALS = array('dog', 'cat', 'bird');
echo ANIMALS[1]; // outputs 'cat'
// Constant arrays
define('ANIMALS', array(
'dog',
'cat',
'bird'
));
echo ANIMALS[1]; // outputs 'cat'
?>
What Is Php
Note:
As opposed to defining constants using define(), constants defined using the
const
keyword must be declared at the top-level scope because they are defined at compile-time. This means that they cannot be declared inside functions, loops, if
statements or try
/ catch
blocks. Basic Syntax
PHP basic syntax is nothing it just how to start writing PHP script. Basically, it gives the basic structure of PHP. There are three methods to start writing PHP scripts.
- The basic syntax of PHP starts with <?php and ends with ?>.
- And also used short tag starts with <? and ends with ?>.
- It's also a valid syntax '< script language='php' and ends with </script>.
Php Syntax List
The PHP script could be placed anywhere in the HTML document.
PHP Basic Syntax Example
In the above example, all three method are shown. Every type of structure has one echo statement that will print something on the screen.
The start and end code must with the same tag, for example the code cannot start with <?php and end with</script>.
PHP semicolon
The semicolon (;) signifies the end of a PHP statement. There should be a semicolon after each line.
PHP semicolon Example
In the above example there are four echo statements and at the end of each echo statement semicolon must be there.
Example of semicolon
Output
Parse error: syntax error, unexpected '$roll_of_student'
Php Program Structure
If you did not terminate any PHP statement then error message will occur as shown in above.